USING METAL OXIDE MARKERS FOR LARVAL FEEDING AND NUTRITION STUDIES  

Live rotifers and Artemia nauplii are necessary feeds for most cultured marine fish larvae. Live feeds are expensive and can be nutritionally variable. Development of microparticulate diets (MPD's) that would be readily accepted could reduce reliance on live feeds. The oxides of yttrium and rare earth metals of the lanthanide series have been shown to be useful as inert consumption and digestion markers for larval fish feeding studies. Artemia nauplii and rotifers readily take up the markers (Yttrium oxide (Y₂O₃), Ytterbium oxide  (Yb₂O₃), Lanthanum oxide  (La₂O₃), and Dysprosium oxide (Dy₂O₃)) to amounts necessary for nutrition studies (>2% dry weight). The markers are also easily incorporated into formulated MPD's. All four markers produce intense emission spectra at characteristic wavelengths when analyzed using inductively coupled plasma - optical emission spectroscopy and only minute amounts are needed in samples for analysis compared to other methods (e.g., 0.020μg and 0.038μg for Y₂O₃ and Dy₂O₃ markers, respectively). We conducted multiple experiments outlined below, aimed at developing methods for using oxide markers for consumption and nutrition experiments.

Experiments:

1.      Determination of marker uptake and depletion by rotifers and Artemia nauplii and rotifer and Artemia nauplii survival during the marking process.

2.      Validation of a method to determine apparent protein digestibility of Artemia nauplii and an experimental MPD.

3.      Acceptability of Y₂O₃, Yb₂O₃, La₂O₃ and Dy₂O₃ in different base diets by the larvae of three different marine fish species.

4.      Histologically determined if repeated feedings of marked live feed over time damaged larval fish GI tracts.

Results: 1. Artemia and rotifers readily take up all four markers to concentrations required for nutrition and consumption studies and survival was good during the marking process, ~ 90% or greater. Live feeds do deplete marker after being fed out, however, this can be accounted for. 2. By comparing protein and maker ratios in the feed, larvae and feces we were able to determine differences in apparent digestibility of Artemia nauplii and a MPD. 3. There were some significant differences in consumption of differently marked base diets suggesting larvae were selecting or avoiding feeds based on the marker employed. These differences were species and feed type specific. 4. The markers do not appear to harm sablefish larvae. The ingested markers did not pass into the mucosa or submucosal tissues of the stomach or intestine, and remained free, strictly within the lumen of these organs